1. Field of the Invention
This invention relates to a polishing member, such as a polishing sheet or a polishing disk, for polishing an end face of an optical fiber connector ferrule, and a process for producing the polishing member.
2. Description of the Prior Art
End faces of optical connector ferrules in which, for example, optical fibers have been inserted and secured have heretofore been polished by utilizing polishing members or polishing slurries. In such cases, since different materials are polished at the end face of the optical fiber connector ferrule, satisfactory polishing results cannot always be obtained in the aspect of optical transfer loss at the end face, or the like.
Specifically, the end face of the optical fiber connector ferrule contains different materials including various kinds of ceramics, such as a glass material, alumina, and zirconia. In order for the optical transfer loss to be prevented, the different materials must be polished uniformly. Particularly, heretofore, it has not always been possible to perform the polishing such that the surface smoothness of the ferrule surface and the optical fiber surface may be kept high, such that a difference in level between the ferrule surface and the optical fiber surface may not occur, and such that the high return loss characteristics may thereby be obtained.
An example of a polishing member has been proposed in, for example, Japanese Unexamined Patent Publication No. 8(1996)-336758. The proposed polishing member comprises a substrate and a polishing layer overlaid on the substrate by applying a coating composition, which comprises a binder and colloidal silica particles dispersed in the binder, the colloidal silica particles having a mean particle size falling within the range of 0.1 xcexcm to 0.1 xcexcm.
The polishing member as described above is produced with a coating composition dispersing apparatus, a coating apparatus, a calendering apparatus which may be employed when necessary, a heat treatment apparatus, a slitting apparatus, a wind-up apparatus, and the like.
With the conventional polishing member described above, the colloidal silica particles having a mean particle size falling within the range of 0.01 xcexcm to 0.1 xcexcm are dispersed in the polishing layer. Non-colloidal silica particles (un-agglomerated silica particles) having the fine particle size described above have the problems in that they cannot be easily dispersed in the binder and a solvent and, therefore, the coating composition for forming the polishing layer cannot be prepared. Therefore, in the conventional polishing member described above, the colloidal silica particles are utilized. However, the use of the colloidal silica particles is disadvantageous from the view points of the productivity, the cost, and the like.
In cases where fine polishing particles of alumina, or the like, other than silica are utilized, if they have a high Mohs hardness, there is the risk that scratches will occur on the end face of the optical fiber, and a difference in level will occur between the end face of the optical fiber and the end face of the ferrule. In cases where fine polishing particles of alumina, or the like, other than silica, which have a low Mohs hardness are utilized, there is the risk that a high polishing power cannot be obtained, the surface cannot be polished smoothly, and the return loss will become large. In cases where polishing particles having a small mean particle size are utilized, the problems occur in that a high polishing power cannot be obtained, and a long time will be required to perform the polishing. In cases where polishing particles having a large mean particle size are utilized, the problems occur in that flaws (scratches) occur on the polished surface, the surface will become rough and will have a low flatness, and finish polishing with good quality cannot be achieved.
As for techniques for polishing with a polishing slurry, an alkaline polishing slurry has heretofore been utilized. The technique for utilizing the alkaline polishing slurry is effective for lowering the viscosity, but has the problems in that neutralization, and the like, must be performed at the time of waste liquid treatment.
The primary object of the present invention is to provide a polishing member, in which dispersibility of fine silica particles is enhanced and which is suitable for polishing an end face of an optical fiber connector ferrule.
Another object of the present invention is to provide a process for producing the polishing member.
The present invention provides a polishing member for use in polishing of an end face of an optical fiber connector ferrule, the polishing member comprising a substrate and a polishing layer, which is overlaid on the substrate and which comprises a binder and fine polishing particles dispersed in the binder,
wherein agglomerated fine silica particles having a mean particle size falling within the range of 0.1 xcexcm to 4 xcexcm are utilized as the fine polishing particles contained in the polishing layer, and a thickness of the substrate falls within the range of 25 xcexcm to 150 xcexcm.
In the polishing member in accordance with the present invention, the agglomerated fine silica particles, in which fine silica particles have been agglomerated, are utilized directly as the fine polishing particles contained in the polishing layer. The agglomerated fine silica particles have a mean particle size falling within the range of 0.1 xcexcm to 4 xcexcm. The agglomerated fine silica particles should preferably have a mean particle size falling within the range of 0.5 xcexcm to 4 xcexcm, and should more preferably have a mean particle size falling within the range of 0.9 xcexcm to 4 xcexcm. Colloidal silica particles are not utilized as the fine polishing particles contained in the polishing layer.
From the view points of lubrication effects and cooling effects, the polishing with the polishing member in accordance with the present invention should preferably be performed while a polishing liquid, which is constituted of water or a silica slurry, is being supplied onto a surface of the polishing layer. In such cases, the polishing liquid should preferably be free from a base or an acid. In cases where the polishing liquid is constituted of the silica slurry, the silica material contained in the silica slurry should preferably be identical with the silica material of the agglomerated fine silica particles, which are contained in the polishing layer.
In the polishing member in accordance with the present invention, a dry thickness of the polishing layer should preferably fall within the range of 5 xcexcm to 15 xcexcm. Also, in the polishing layer, the proportion of the binder per 100 parts by weight of the agglomerated fine silica particles should preferably fall within the range of 30 to 100 parts by weight.
The present invention also provides a process for producing a polishing member for use in polishing of an end face of an optical fiber connector ferrule, the process comprising the steps of:
i) preparing a coating composition for forming a polishing layer, the coating composition comprising agglomerated fine silica particles having a mean particle size falling within the range of 0.1 xcexcm to 4 xcexcm, a binder, and an organic solvent,
ii) applying the coating composition onto a substrate having a thickness falling within the range of 25 xcexcm to 150 xcexcm, and
iii) drying the applied coating composition to form the polishing layer.
In the process for producing a polishing member in accordance with the present invention, the agglomerated fine silica particles, in which fine silica particles have been agglomerated, are utilized directly as the fine polishing particles contained in the polishing layer. The agglomerated fine silica particles have a mean particle size falling within the range of 0.1 xcexcm to 4 xcexcm. The agglomerated fine silica particles should preferably have a mean particle size falling within the range of 0.5 xcexcm to 4 xcexcm, and should more preferably have a mean particle size falling within the range of 0.9 xcexcm to 4 xcexcm.
Also, in the process for producing a polishing member in accordance with the present invention, the preparation of the coating composition for forming the polishing layer should preferably be performed by dispersing the agglomerated fine silica particles with a sand grinder.
Further, in the process for producing a polishing member in accordance with the present invention, a surface of the polishing layer should preferably be subjected to calendering. In such cases, the linear pressure in the calendering should preferably fall within the range of 50 kg/cm to 300 kg/cm. Also, a calendering roll may be selected from metal rolls, resin rolls, and the like.
With the polishing member in accordance with the present invention, the agglomerated fine silica particles having a mean particle size falling within the range of 0.1 xcexcm to 4 xcexcm are utilized as the fine polishing particles contained in the polishing layer, which is overlaid on the substrate having a thickness falling within the range of 25 xcexcm to 150 xcexcm. When the agglomerated fine silica particles are dispersed in the binder, they are not dispersed to the level of the primary particles. The agglomerated fine silica particles are uniformly dispersed with the sizes of the agglomerated fine silica particles in the binder. The polishing layer, in which the agglomerated fine silica particles are dispersed with the agglomerated particle sizes, has a high film strength and enhanced polishing performance for the polishing of the end face of the optical fiber connector ferrule, and yields few grinding scratches on the end face of the optical fiber.
Specifically, with the polishing member in accordance with the present invention, the end face of the optical fiber connector ferrule can be polished such that no scratch occurs on the polished surface, such that the end of the optical fiber can be formed into a predetermined curved surface shape, and such that no difference in level occurs between the polished surface of the optical fiber (formed from quartz glass, or the like) and the polished surface of the ferrule (formed from zirconia, or the like). As a result, the return loss in optical transfer after the polished end faces are joined to each other can be reduced to at most xe2x88x9250 dB. Also, since no difference in level occurs between the polished surface of the optical fiber and the polished surface of the ferrule, the end face of the optical fiber connector ferrule can be kept free from any dirt.
Further, in the polishing with the polishing member in accordance with the present invention, when necessary, the polishing liquid constituted of water or a silica slurry can be utilized. In cases where the polishing liquid does not contain a base or an acid, waste liquid treatment can be performed easily.
As described above, the thickness of the substrate falls within the range of 25 xcexcm to 150 xcexcm, and the dry thickness of the polishing layer should preferably fall within the range of 5 xcexcm to 15 xcexcm. If the dry thickness of the polishing layer is less than 5 xcexcm, a high durability in the polishing cannot be obtained. For use in practice, it is unnecessary for the polishing layer to have a dry thickness of more than 15 xcexcm. If the thickness of the substrate is less than 25 xcexcm, the substrate will wrinkle and cannot have high suitability for the polishing. If the thickness of the substrate is more than 150 xcexcm, the processing at the time of the application of the coating composition for forming the polishing layer cannot be performed easily, and it will become difficult to flatly attach the polishing member to a support base.
With the process for producing a polishing member in accordance with the present invention, the coating composition for forming the polishing layer is prepared, the coating composition comprising the agglomerated fine silica particles having a mean particle size falling within the range of 0.1 xcexcm to 4 xcexcm, the binder, and the organic solvent. The coating composition is applied onto the substrate having a thickness falling within the range of 25 xcexcm to 150 xcexcm. The applied coating composition is then dried to form the polishing layer. By the utilization of, for example, a sand grinder, the dispersing of the agglomerated fine silica particles in the binder can be performed such that they are not dispersed to the level of the primary particles and can be uniformly dispersed with the sizes of the agglomerated particles in the binder. Therefore, the productivity can be enhanced, and the polishing member can be produced at a low cost. Also, as described above, the film strength of the polishing member can be kept high, and the polishing member having good polishing characteristics for the polishing of the end face of the optical fiber connector ferrule can be obtained.
The present invention will hereinbelow be described in further detail with reference to the accompanying drawing.